This invention relates to improved silane coupling agents. One aspect of the invention relates to sizing compositions for glass fibers that give improved hand and stiffness to sized fiberglass strand, roving, and fabric and improved bonding of such materials to ethylenically unsaturated resins, such as polyesters, when such resins are cured in contact with sized glass fibers.
Organofunctional silanes such as epoxy, amino, mercapto, vinyl, acrylic, and methacrylic functional silanes having at least one readily hydrolyzable group such as an alkoxy or a halogen group, usually two or three such hydrolyzable groups, are known. Such organofunctional silanes have one functional group capable of reacting with an organic resin, and one or more hydrolyzable groups capable of bonding to an inorganic substrate such as silica, fiberglass, or steel. Such coupling agents improve adhesion or bonding between a cured organic matrix and the inorganic substrate and also permit higher loading of finely divided fillers without an excessive loss in the strength of the cured composition. Blends of two or more of such organofunctional silanes, wherein both silanes are reactive. with an organic resin, have been described.
In addition, U.S. Pat. No. 3,702,783 to Hartlein describes a blend of an epoxy functional silane, 3glycidoxypropyl-trimethoxysilane, with an alkyl silane, methyltrimethoxy-silane, for bonding glass to epoxy resins, amino resins, polyamides, and polyacrylates. The methyltrimethoxy-silane is not reactive with the organic resins through its methyl substituent, but is believed to be reactive with such resins through its hydrolyzable methoxy substituents in the presence of an epoxy-functional silane. Thus, the patent describes a blend of two silanes, both of which are reactive with the organic resins with which the silanes are disclosed for use.
U.S. Pat. No. 3,816,235 to Lin discloses a silane coupling agent comprising an N-(2-aminoethyl)-3-amino-propylsilane having three hydrolyzable groups with an alkyl silane such as methyltriethoxysilane for use in a glass fiber sizing composition that also includes a resin formed of maleic anhydride and a conjugated diene, an alkyl acrylate or methacrylate, or a vinyl aromatic monomer. It is believed that the methyltrialthoxysilane is reactive through its ethoxy substituents with the organic resins, particularly resorcinol-aldehyde resins, with which the silanes are disclosed for use.
In the systems described in the two aforesaid patents, it is believed that functional groups that are reactive with alkoxysilanes, such as hydroxyl groups, are present in the organic matrix before or during cure, and that the alkyl-trialkoxysilane components of the blended coupling agents are therefore capable of reacting with the organic matrix.